1. Field of the Invention
The present invention generally relates to optical devices, and more particularly, the present invention relates to the fabrication of optical devices having integrated optical waveguides.
2. Description of the Related Art
Optical integrated circuit (OIC) and optical bench fabrication often involves transferring patterns to a substrate. These patterns may be used to form a variety of structures to include conductive circuit lines, planar waveguides, mesas and recesses. Typically, the desired structures are formed using lithography. Lithography may be achieved by techniques such as photolithography, x-ray lithography and e-beam lithography.
In photolithography, for example, a layer of photo-reactive film, known as photoresist, may be formed over the substrate. A photolithographic mask containing the image of a desired pattern is then placed in contact with the photoresist film. Radiation of a wavelength to which the photoresist is sensitive is incident upon the mask. The radiation passes through the transparent areas of the mask and the exposed areas of the photoresist are reactive to the radiation. The photoresist film is then chemically developed, leaving behind a pattern of photoresist substantially identical to the pattern on the mask.
The patterned photoresist on the substrate may be used in a variety of applications to form the structures referenced above. For example, a pattern photoresist may act as a mask for selective etching of a substrate. This selective etching may be used to fabricate recesses and as mesas in the substrate. In OIC and optical bench technologies, the mesas and recesses may be used for a variety of purposes, including passive alignment of optical elements.
The above described photolithographic process is often referred to as contact printing, because the mask is placed in contact with the substrate. Contact printing has facilitated the fabrication of highly integrated structures in both electrical and optical integrated circuits. However, conventional contact printing techniques have certain limitations. For example, conventional contact printing techniques generally are useful only in processing flat substrates. If a substrate has a relief (i.e. has a non-planar topography) it is exceedingly difficult to fabricate structures on the substrate by flat conventional contact printing techniques. To this end, conventional photolithographic masks are substantially flat. As a result, it is exceedingly difficult to place the mask in contact with, or in close enough proximity to, all points on the surface of a substrate to enable accurate image projection onto the substrate. In regions of the substrate where the photolithographic mask is not in contact with, or in close enough proximity to, the substrate, diffractive effects result in poor resolution and ultimately a poor transfer of the pattern from the mask to the photoresist.
The above referenced limitations of image lithography processing typically result in inaccurate location and spacing of features in a multi-level substrate. These inaccuracies are unacceptable as the integration of various elements at multiple levels in OIC""s and optical bench technologies gains industry acceptance. Accordingly, what is needed are optical integrated circuits and optical benches which incorporate a variety of features at multiple levels which overcome the inaccuracies of conventional structures and methods of manufacture as referenced above.
According to an aspect of the present invention, an optical device is fabricated having at least one integrated waveguide and at least one micro-machined feature. Although not so limited, exemplary micro-machined features include grooves, recesses and inclined surfaces formed in the substrate surface. A mask layer is deposited over a surface of a substrate structure, and the mask layer is patterned to obtain a mask pattern over the surface of the substrate structure. A first etching process is then carried out for obtaining the at least one integrated optical waveguide core at the surface of the substrate structure, and a second etching process is carried out for obtaining the at least one micro-machined feature at the surface of the substrate structure. Advantageously, the same previously formed mask pattern is used as a mask in both the first and second etching processes, thereby resulting in accurate positioning of the waveguide core relative to the micro-machined feature.